The present invention pertains to devices and methods for sharpening scissors, in particular scissors designed for personal hair cutting. Hair scissors, or shears as they are often called, are precise instruments that require careful periodic sharpening to provide quality performance. The cutting surfaces of such scissors may be flat but are more commonly curved in more than one direction to optimize cutting with a minimum of force and drag on the hair. In particular, it is popular for scissor blades to be curved, from root of the cutting surface near the handle to the tip. Blades with an 600 to 1000 millimeter blade shape radius are very popular and are used on many of the best scissors for hair cutting. Similarly, the scissor cutting surface is often convex shaped. The result, in a scissors with a radius and convex shape, is a complex cutting surface.
When scissors blades are sharpened, it is critical that the existing shape of the cutting surfaces be maintained. This is relatively simple for scissors with straight and flat blades, but this requirement is very difficult to meet with blades with complex blade surfaces such as found on a scissors with both a blade radius and convex face. Available sharpening devices have flat working surfaces. To properly sharpen a complex curved scissors blade with a flat sharpening device requires very precise and complicated movements. In many instances, improper sharpening results in flats or irregularities in the scissors shape and cutting surfaces and, effectively, a destroyed scissors blade.
There are prior art devices that attempt to provide accurate sharpening of curved scissor blades. For example, U.S. Pat. No. 7,118,466 to Laney provides a curved guide bar to attempt to limit the movement of a clamped scissor blade to a single preselected shape. However, at best, the Laney device is still dependent on proper user operation and without careful operation a blade can be ruined during sharpening. Also, due to the limitations of the Laney guide bar, it is difficult to sharpen any blade—such as a previously improperly sharpened blade—that deviates from the predefined shape.
There remains a demand for a scissors sharpening device that reduces the difficulty in sharpening curved scissor blades. Preferably, such a device will allow for sharpening blades with irregularities such as variable blade radius that have been produced from prior improper sharpening and that will duplicate the many flat and curved blades manufactured.